The invention relates to a device for counting overvoltage surges discharged by a gapless overvoltage arrester.
Such a surge counter has been published in an article by Breder et al. "Supervision of Gapless Zinc-Oxide Surge Arresters" Conference on Lightning+Power Systems, London 1984 (conference Publication No. 236, IEE). In the gapless overvoltage arrester described in this article, overvoltage surges are detected by means of a sensing head which detects the discharge current carried in a ground return line of the overvoltage arrester. The sensing head is followed by a counting mechanism which contains a counter which records the number of overvoltage surges and a switch which precedes the counter. Above a threshold value of the discharge current, this switch establishes for a brief time an effective connection between the sensing head and the counter. This makes it possible to detect each overvoltage surge accurately. However, the timing sections used in this connection are comparatively expensive and have a dead time which is dependent on the time characteristic of the discharge current.
As noted in the Breder et al. paper, a device for counting overvoltage surges permits monitoring of possible surge arrester degradation. Although gapless overvoltage arresters have proven fairly reliable, it is advisable to count the number of overvoltage surges since each overvoltage surge may cause a small degree of degradation of non-linear metal oxide resistors provided within the gapless overvoltage arrester.